qt - 扩展/连接多个 ListModel 的声明方式

Question

我想构建多个 ListModel，它们都将以公共(public)元素开头。我想填充另一个 ListModel 中的剩余元素。

例子:列表模型(一):

COMMON A
COMMON B
COMMON C
A1
B1
C1

列表模型(2):

COMMON A
COMMON B
COMMON C
A2
B2
C2

有没有办法以声明方式“合并”或扩展两个 ListModel？

到目前为止，我正在动态地进行:

import QtQuick 2.9
import QtQuick.Window 2.2

Window {
    width: 480
    height: 320
    visible: true

    ListModel {
        id: commonModel
        ListElement { value: "COMMON A" }
        ListElement { value: "COMMON B" }
        ListElement { value: "COMMON C" }
    }

    ListModel {
        id: model1
        ListElement { value: "A1" }
        ListElement { value: "B1" }
        ListElement { value: "C1" }
    }

    ListModel {
        id: model2
        ListElement { value: "A2" }
        ListElement { value: "B2" }
        ListElement { value: "C2" }
    }

    ListView {
        anchors.fill: parent
        model: commonModel // here I would like to directly specify the "concatenated" model

        delegate: Text { text: model.value}

        // dynamic part that I want to avoid
        readonly property var additionalModel: model2
        Component.onCompleted: {
            for (var i = 0; i < additionalModel.count; ++i) {
                var elt = additionalModel.get(i)
                model.append(elt)
            }
        }
    }
}

---

编辑:换句话说，我想做一些像这样简单的事情:

// MyModel.qml
ListModel {
    ListElement { value: "COMMON A" }
    ListElement { value: "COMMON B" }
    ListElement { value: "COMMON C" }
}

能够根据需要在另一个组件中扩展它:

ListView {
    model: MyModel {
        // keep original elements from MyModel and add custom "component-related" elements
        ListElement { value: "OTHER A" }
        ListElement { value: "OTHER B" }
        ListElement { value: "OTHER C" }
    }
}

但这似乎不可能，因为我收到以下错误:

Cannot assign to non-existent default property

Answer 1

让我们从修补错误开始。它来自这里:

model: MyModel {
    ListElement { role_value: "OTHER A" }
    ListElement { role_value: "OTHER B" }
    ListElement { role_value: "OTHER C" }
}

要获得这种行为，您需要设置 MyModel 的属性之一。到 default property .平凡的，像

//  MyModel.qml
ListModel {
    default property list<ListElement> otherModels

    ListElement { role_value: "COMMON A" }
    ListElement { role_value: "COMMON B" }
    ListElement { role_value: "COMMON C" }
}

//  Main.qml
import QtQuick 2.0
import QtQuick.Window 2.2

Window {
    ListView {
        model: MyModel {
            // these should be auto-assigned to the default property      
            ListElement { role_value: "OTHER A" }
            ListElement { role_value: "OTHER B" }
            ListElement { role_value: "OTHER C" }
        }
    }
}

通常，对于其他类型，这可以正常工作。但是ListElement是一个特例。如果你尝试运行上面的代码，你可能会得到一个错误:

Cannot assign to non-existent property "role_value"

Documentation暗示 ListElements只能在 ListModels 下定义.据我所知，这似乎是唯一可行的解​​决方法。这意味着将默认属性更改为 list<ListModel>并将用法更改为

ListView {
    model: MyModel {
        // ListModel is auto-assigned to the default property
        ListModel {
            ListElement { role_value: "OTHER A" }
            ListElement { role_value: "OTHER B" }
            ListElement { role_value: "OTHER C" }
        }
    }
}

这是一个最小的完整示例:

//  MyModel.qml
import QtQuick 2.0

ListModel {
    id: model
    default property list<ListModel> otherModels

    ListElement { role_value: "COMMON A" }
    ListElement { role_value: "COMMON B" }
    ListElement { role_value: "COMMON C" }

    //  called everytime a model is append to otherModels
    onOtherModelsChanged: {
        //  add ListElements from the last otherModels to this model
        var i = otherModels.length - 1;
        if (i < 0) return;

        for (var j = 0; j < otherModels[i].count; j++)
            model.append(otherModels[i].get(j));
    }
}


//  Main.qml
import QtQuick 2.6 
import QtQuick.Window 2.2      //  Window
import QtQuick.Controls 2.2    //  ItemDelegate

Window {
    visible: true
    width: 640
    height: 480

    ListView {
        anchors.fill: parent
        model: MyModel {
            ListModel {
                ListElement { role_value: "OTHER A" }
                ListElement { role_value: "OTHER B" }
                ListElement { role_value: "OTHER C" }
            }
        }

        delegate: ItemDelegate {
            text: role_value
            width: parent.width
        }
    }
}

^{See a more sophisticated demo on Github.}

default property list<ListModel>和执行 onOtherModelsChanged允许将多个模型“连接”到基础模型上。

成功截图:

如 augre 所述，在仅连接一个 模型的情况下，您可以将属性简化为 default property ListModel otherModel并且有

onOtherModelChanged: {
    if (otherModel === undefined) return;
    for (var i = 0; i < otherModel.count; i++)
        model.append(otherModel.get(i));
}